This invention relates to a magnetic core comprised of a stack of plates which extend mainly along a single axial direction and which contact one another with the main surfaces thereof, and of which the stack cross-section has as envelope thereof a closed curve without discontinuities, which is of approximately ellipse shape, which has a first symmetry axis which lies in parallel relationship with the plates and a second symmetry axis at right angle thereto, whereby the spacing b between the intersection points of the curve with the second symmetry axis is markedly wider than the spacing a between the intersection points of the curve with the first symmetry axis.
A magnetic core is particularly used as part, for example as leg, of a transformer core, or as core of a choke coil.
Such a core is then surrounded by one or two windings. In that case where said magnetic core is one leg of a transformer core, it is generally surrounded by two windings, an innermost low-voltage winding and an outermost high-voltage winding.
Even if as already stated above, magnetic cores as a rule and the magnetic core according to the invention particularly may have various uses, for clearness' sake the use as leg of a transformer core will be mainly mentioned. This does not however exclude other uses according to the invention, and it will be clear for the man of the art that the principle defined in connection with the leg of a transformer core, is also valid for the other possible uses.
Various kinds of legs are known, notably legs which have at right angle to the axial direction, a cross-section with a circle as envelope and fill to the most said circle, and legs which have at right angle to the axial direction, a rectangular, possibly square cross-section.
For the sake of convenience said legs will be called hereinafter round and rectangular legs, respectively.
As well here as hereinafter, the wording "envelope" should be understood as the closed flowing curve, which has thus no discontinuities, which goes through all of the projecting angular points of that core cross-section which lies at right angle to the axial direction.
It is to be noted that it is generally conventional, as further explained hereinafter, to provide the required place for axially-located open feeders of low-voltage foil windings by means of a flattening of the leg cross-section, that is with a single-sided lowering of the stacking height of the stack. For the determination of the envelope, abstraction is made of said flattening, as this will be further explained hereinafter.
It is known to the man of the art how in the cases of round and rectangular legs, an economically optimum composition of the leg is to be reached and which particular specific advantages and disadvantages both said conventionally known embodiments may have.
There is known from FR-A-1,493,312, a transformer core of the above-defined kind wherein said envelope is ellipse-shaped or approximately of ellipse shape. The leg of such a transformer core, called hereinafter ellipse-shaped for convenience sake, offers relative to the round and rectangular legs, some advantages, allows particularly a more economic structure of the transformer for defined technical specifications, combines some advantages of the round and rectangular legs, and limits the disadvantages thereof.
Both the round and the known ellipse-shaped legs have however the disadvantage, that any change in the required cross-section of the magnetic core and consequently of the circle diameter or at least of one axis of the ellipse, causes a change in the required plate widths and mostly of the templates which are used during the manufacture and which have to relate with said envelopes.